reify yields the wrong type in the presence of functional dependencies

reify yields an incomplete type in the following program.

{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE FunctionalDependencies #-}
module B where
import Language.Haskell.TH as TH
import Language.Haskell.TH.Syntax as TH

class C a b | a -> b where
  yo :: a -> IO b

instance C Bool Int where
  yo = undefined

t3 :: IO ()
t3 = do
  x <- yo True
  $(do addModFinalizer $ TH.reify 'x >>= runIO . print
       [| return () |]
   )

$ inplace/bin/ghc-stage2 B.hs -fforce-recomp
[1 of 1] Compiling B                ( B.hs, B.o )
VarI x_1627401898 (VarT a_1627404604) Nothing

The problem seems to be that finalizers run before functional dependencies are considered.

Hacking ghc to run finalizers after simplifyTop produces the expected output instead:

$ inplace/bin/ghc-stage2 B.hs -fforce-recomp
[1 of 1] Compiling B                ( B.hs, B.o )
VarI x_1627404863 (ConT GHC.Types.Int) Nothing

Would anyone object to running finalizers after simplifyTop? This implies that finalizers shouldn't add definitions (with addTopDecls) which depend on simplifyTop to be type-checked.

Another option is to call simplifyTop before and after running finalizers. But is it safe to do so?

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	goldfire, mboes, simonpj
Operating system
Architecture